An Analysis of the K I λ7698 Line Profile in the Halo Turnoff Star HD 84937 and Its Implications for Lithium Isotopic Studies

摘要

The line profile of the resonance line of K I at 7698 ? has been analyzed in the halo turnoff star HD 84937, using a high-resolution (λ/Δλ = 110,000), high signal-to-noise ratio (S/N = 550) spectrum. Three different groups have reported detecting 6Li in this star, based on a red asymmetry in the Li I λ6707 line profile (6Li displays an isotopic shift of about 0.15 ? to the red, relative to 7Li, in this line). It is possible, however, that convection could introduce this red asymmetry by mass motions of 7Li in the star's atmosphere. At the metallicity of HD 84937, the K I resonance line at 7698 ? is expected to have a similar line strength to the Li I λ6707 feature, and both these lines are resonance transitions. In addition, both potassium and lithium have similar first ionization potentials. The result of these similarities is that the Li I and K I lines are formed at nearly identical regions in the atmosphere of HD 84937. This study presents a line profile analysis of the K I line, which has negligible isotopic splitting and is effectively a single-component line, in HD 84937. Any possible convective motions of sufficient magnitude to produce a spurious detection of 6Li should also produce detectable asymmetries in the K I line. No such asymmetries are found here, strengthening the case that the previously reported detections of 6Li in HD 84937 are real.